This invention relates generally to gas-insulated electrical apparatus, and more particularly to gas-insulated electrical apparatus including provisions for inserting monitoring or inspection members into the interior of the apparatus without introducing contamination particles or permitting the escape of the insulating gas.
Gas-insulated electrical apparatus typically comprises an outer enclosure, or sheath, at low or grounded electrical potential, and an electrode disposed within the enclosure at high potential with respect to the enclosure. The electrode may, for example, be at system voltages ranging from 138 KV to 1100 KV. An electrically insulating gas, typical of which is sulfur hexafluoride or mixtures containing sulfur hexafluoride, is disposed within the enclosure and electrically insulates the inner-disposed electrode from the outer enclosure.
The above-described electrical apparatus is typically elements either in a gas-insulated substation or is a transmission line. When a fault occurs in either the substation or the transmission line, there are circumstances where it may be desirable to have the ability to make an inspection of the faulted area to evaluate the damage and decide whether the section needs to be replaced or repaired, or whether it has the ability to be connected back into electrical service. To do this in an efficient manner, it may be desirable to have an optical inspection system which allows a visual observation device to be inserted through the outer electrode, or sheath, without removing the insulating gas, and after the inspection be able to seal the inspection hole with a gas-tight fitting. The inspection system should preferably not introduce deleterious contamination particles into the equipment during any of the cutting, inspecting, or sealing operations.